Continuous preparation process of p-chloro-o-cresol

Abstract

The invention relates to the technical field of organic synthesis, and discloses a continuous preparation process of p-chloro-o-cresol, which comprises the following steps: mixing o-cresol and dichloroethylene, reacting with sulfuryl chloride in the presence of a proper catalyst, and controlling the reaction process by adopting staged sulfuryl chloride addition rate to avoid the occurrence of polychlorination side reaction. The reaction temperature is kept between 5 DEG C and 15 DEG C, products are effectively separated and recycled through a rectification and tail gas treatment system, and generation of by-products is reduced. The process has the advantages of mild reaction conditions, lower catalyst dosage, higher product purity and better environmental protection effect, is suitable for large-scale industrial production, and has higher resource utilization efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, in particular to a continuous preparation process of p-chloro-o-cresol. Background Art

[0002] As an important organic chemical raw material, p-chloro-o-cresol (4-chloro-2-methylphenol) is widely used in medicine, pesticides, solvents, dyes, pigments, mildew inhibitors, surfactants, fragrances and other fields. It is not only an important intermediate in organic synthesis, but also can be used to synthesize important chemicals such as 2-methyl-4-chloropropionic acid and 2-methyl-4-chlorobutyric acid. Due to its importance, the development of efficient and economical synthesis methods is of great significance to improve production efficiency.

[0003] At present, there are several problems in the traditional synthesis method of para-chloro-o-cresol, which are mainly reflected in aspects such as low yield, harsh reaction conditions and poor reaction selectivity. For example, some existing synthetic methods first mix para-chlorobenzoic acid and o-cresol, add a small amount of pyrophosphoric acid as a condensation catalyst, and react for several hours to generate para-chloro-o-cresol under 120-130 ℃ of conditions. The yield of this method is relatively low, and the reaction conditions are relatively harsh, which limits its application in industry. In addition, there is also a method for generating para-chloro-o-cresol by mixing para-chlorobenzoic acid and o-cresol, adding a reducing agent (such as sodium sulfite) and an oxidant (such as hydrogen peroxide) under alkaline conditions. However, the conditions of this reaction are relatively complicated, and the by-products produced in the reaction are more, resulting in a lower purity of the product.

[0004] Another common synthesis method is to conduct a chlorination reaction by passing chlorine gas under the catalysis of Lewis acid (such as lithium chloride, copper chloride, aluminum chloride) to produce a mixture of 4-chloro-2-methylphenol, 6-chloro-2-methylphenol and 4,6-dichloro-2-methylphenol. This method has low reaction selectivity, resulting in serious polychlorination and a high isomer content, which affects the quality and purity of the product.

[0005] Therefore, the existing technology has problems such as harsh reaction conditions, poor reaction selectivity, and low yield. A new, simple and efficient synthesis method is urgently needed to solve these technical problems and improve the production efficiency and product quality of 4-chloro-o-cresol. Summary of the invention

[0006] In view of the deficiencies of the prior art, the present invention provides a continuous preparation process of 4-chloro-o-cresol, which has mild reaction conditions, high selectivity, no polychlorination phenomenon, low isomer content and high crude product yield.

[0007] To achieve the above object, the present invention is implemented by the following technical scheme: a continuous preparation process of 4-chloro-o-cresol, comprising the following steps:

[0008] a) adding ethylene dichloride to molten o-cresol and adding a catalyst;

[0009] b) Under the temperature condition of 5 to 15° C., controlling the rate of addition of sulfuryl chloride according to the reaction stage, specifically comprising:

[0010] In the first stage, sulfuryl chloride is added at a rate of 6-15 kg / min;

[0011] In the second stage, sulfuryl chloride is added at a rate of 2 to 5 kg / min;

[0012] In the third stage, sulfuryl chloride is added at a rate of 0.5 to 1.5 kg / min;

[0013] c) After the reaction is completed, the reaction liquid is distilled and purified to obtain p-chloro-o-cresol.

[0014] Preferably, the catalyst is one of diphenyl sulfide, ferric chloride or aluminum chloride.

[0015] Preferably, in step b), the first stage is 1 to 4 hours after the addition of sulfuryl chloride is started, the second stage is 5 to 7 hours after the addition of sulfuryl chloride is started, and the third stage is the remaining time; the total reaction time is controlled to be 8 to 15 hours.

[0016] Preferably, in the first stage, the rate of addition of sulfuryl chloride is 9 kg / min; in the second stage, the rate of addition of sulfuryl chloride is 3 kg / min; and in the third stage, the rate of addition of sulfuryl chloride is 1 kg / min.

[0017] Preferably, in step a), the mass ratio of ethylene dichloride to o-cresol is 1-3:1-4.

[0018] Preferably, in step a), the mass ratio of ethylene dichloride to o-cresol is 1:1.1.

[0019] Preferably, in step b), the mass ratio of the added sulfuryl chloride to o-cresol is 1-2:0.5-1.5.

[0020] Preferably, in step b), the mass ratio of the added sulfuryl chloride to o-cresol is 1.275:1.

[0021] The present invention also provides a continuous preparation system of p-chloro-o-cresol, comprising:

[0022] A reaction kettle is used to mix o-cresol, ethylene dichloride, a catalyst and sulfuryl chloride and react under controlled temperature conditions;

[0023] A degassing device, connected to the reactor, is used to remove volatile gases generated during the reaction and reduce pollution;

[0024] A distillation tower, connected to the degassing device, is used to separate the reaction liquid by distillation, extract pure para-chloro-o-cresol, and reflux the unreacted light components to the reactor;

[0025] The tail gas treatment unit is used to carry out multi-stage adsorption, absorption and drying treatment on the tail gas generated during the reaction.

[0026] Preferably, the tail gas treatment device includes a secondary molecular sieve device, a tertiary falling film water absorption device, a secondary sulfuric acid drying device, a refrigeration recovery device and a secondary alkali absorption device;

[0027] The reactor and the degassing reactor are connected to the secondary molecular sieve through pipelines, and the tail gas in the reactor and the degassing reactor is sent to the secondary molecular sieve device for adsorption; the liquid after adsorption treatment by the secondary molecular sieve device is returned to the reactor;

[0028] The secondary molecular sieve device is connected to the tertiary falling film water absorption device through a pipeline, and the tail gas treated by the secondary molecular sieve device is sent to the tertiary falling film water absorption device for treatment;

[0029] The three-stage falling film water absorption device is connected to the two-stage sulfuric acid drying device through a pipeline, and the tail gas treated by the three-stage falling film water absorption device is sent to the two-stage sulfuric acid drying device for treatment;

[0030] The secondary sulfuric acid drying device is connected to the refrigeration recovery device through a pipeline, and the tail gas treated by the secondary sulfuric acid drying device is sent to the refrigeration recovery device for treatment;

[0031] The refrigeration recovery device is connected to the secondary alkali absorption device through a pipeline. The tail gas treated by the refrigeration recovery device is treated by the secondary alkali absorption device and then discharged.

[0032] The present invention provides a continuous preparation process of 4-chloro-o-cresol. It has the following beneficial effects:

[0033] 1. The preparation process provided by the present invention can realize the para-chlorination reaction of o-cresol by accurately controlling the reaction conditions, thereby maximizing the yield and selectivity of o-chloro-o-cresol and reducing the generation of by-products. This process greatly improves the purity of the target product and reduces the waste of resources in the production process.

[0034] 2. The reaction conditions of the present invention are milder, avoiding possible side reactions at high temperatures, thereby improving the safety and stability of the reaction. This mild condition helps to shorten the reaction time and improve the overall production efficiency.

[0035] 3. The present invention can reduce the amount and cost of catalyst while ensuring efficient catalytic reaction by controlling the amount of catalyst used. Reasonable catalyst dosage makes the reaction more efficient and helps reduce the generation of unnecessary by-products.

[0036] 4. The process of the present invention effectively recovers and treats the waste gas generated during the reaction process through an improved tail gas treatment system, reduces the emission of harmful gases, and meets environmental protection requirements. The design of the distillation and tail gas treatment device can reduce environmental pollution and has high environmental protection.

[0037] 5. The continuous preparation process provided by the present invention has high production stability and repeatability, and is suitable for large-scale industrial production. The optimized reaction and separation processes simplify the operation, improve production efficiency, and reduce production costs.

[0038] 6. The process of the present invention is simple and the reaction conditions are mild. The process is controlled by the reaction and has high selectivity, so that o-cresol is preferentially para-chlorinated, the reaction is sufficient, the selectivity is high, there is no polychlorination phenomenon, the crude product contains low amounts of phenol and its isomers, the yield is high, and it is more conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention specification.

[0041] Please see attached Figure 1 The present invention provides a continuous preparation process of 4-chloro-o-cresol, comprising the following steps:

[0042] S1. Raw material preparation and catalyst addition: First, ethylene dichloride and o-cresol are mixed and heated until the o-cresol is molten. Then, an appropriate amount of catalyst (such as diphenyl sulfide, ferric chloride or aluminum chloride) is added to promote the reaction.

[0043] S2. Gradually add sulfuryl chloride: At a reaction temperature of 5-15°C, add sulfuryl chloride to the reaction system in stages according to the progress of the reaction. In the first stage, add sulfuryl chloride quickly to start the reaction, in the second stage, reduce the addition rate appropriately to avoid the formation of by-products, and in the third stage, add sulfuryl chloride slowly to ensure complete reaction without over-chlorination.

[0044] S3, distillation and purification: After the reaction is completed, the reaction liquid is separated by a distillation tower to purify para-chloro-o-cresol. The distillation process can effectively remove unreacted raw materials and solvents, and improve the purity and yield of the target product.

[0045] Each step of the process of the present invention is described in detail below.

[0046] According to the technical solution of the present invention, step S1, preparation of raw materials and addition of catalyst:

[0047] First, o-cresol (2-methylphenol) and ethylene dichloride (C 2 H 4 Cl 2 ) need to be mixed in a specific mass ratio. Specifically, the mass ratio of ethylene dichloride to o-cresol is 1 to 3:1 to 4, preferably 1:1.1. The selection of this ratio is based on the solubility of the reactants and the role of ethylene dichloride as a solvent, which can effectively promote the dissolution of o-cresol, thereby making the reaction more sufficient. The addition of ethylene dichloride not only helps to dissolve o-cresol, but also provides the necessary reaction medium for the chlorination reaction of sulfuryl chloride, thereby improving the efficiency of the reaction.

[0048] In this step, o-cresol needs to be heated to a molten state. Usually, the melting point of o-cresol is 32°C, so o-cresol can be melted by heating it to 40-60°C. At this time, o-cresol is in a liquid state and is more easily mixed with ethylene dichloride and reacted with a catalyst. In addition, the temperature needs to be controlled during the reaction so that the mixture of o-cresol and ethylene dichloride is kept within a suitable temperature range to ensure that subsequent reactions proceed smoothly.

[0049] In order to promote the reaction and improve the selectivity of para-chloro-o-cresol, a catalyst needs to be added. In the present invention, the catalyst can be diphenyl sulfide, ferric chloride (FeCl 3 ) or aluminum chloride (Al Cl 3 ). The amount of catalyst added is 1-3% of the mass of o-cresol, and it needs to be stirred evenly to ensure that the catalyst can be evenly distributed in the reaction system to play a catalytic role. The role of the catalyst is to promote the reactivity of o-cresol, especially in the subsequent sulfuryl chloride (SO 2 Cl 2 ) is added, the catalyst will improve the reaction efficiency of o-cresol and sulfuryl chloride.

[0050] According to the technical solution of the present invention, the gradual addition of sulfuryl chloride in step S2:

[0051] In step S2, the reaction temperature is controlled between 5 and 15°C. This temperature range helps to ensure the smooth progress of the reaction and inhibit side reactions that may occur at high temperatures. Specifically, too high a temperature will cause the reaction to be too intense, thereby producing too many by-products or polychlorinated products, while too low a temperature may cause the reaction to proceed slowly, affecting the reaction efficiency.

[0052] Sulfuryl chloride is added to the reaction system in stages in step S2, specifically including three stages of addition rate control. The addition rate setting of each stage is adjusted according to the different stages of the reaction process, the purpose is to ensure that the chlorination reaction can find a balance between selectivity and yield and avoid unnecessary side reactions.

[0053] The first stage (0 to 4 hours): In the initial stage of the reaction, sulfuryl chloride is added at a relatively high rate. The specific addition rate is 6 to 15 kg / min, preferably 9 kg / min. In this stage, when sulfuryl chloride is added quickly, the contact between o-cresol and sulfuryl chloride in the reaction system increases, and the chlorine atoms in sulfuryl chloride react with o-cresol by nucleophilic substitution. At this point, the reaction rate is relatively fast, and the generated p-chloro-o-cresol occupies the main product position.

[0054] The second stage (5 to 7 hours): When the reaction is in the middle stage, the addition rate of sulfuryl chloride should be appropriately reduced to 2 to 5 kg / min, preferably 3 kg / min. At this time, as the reaction proceeds, the conversion rate of o-cresol gradually increases, and the addition rate of sulfuryl chloride is appropriately reduced to ensure the selectivity of the reaction. This helps to inhibit the formation of polychlorinated products and ensure the generation of p-chloro-o-cresol.

[0055] The third stage (8 hours later): In the later stage of the reaction, the addition rate of sulfuryl chloride is further reduced to 0.5-1.5 kg / min, preferably 1 kg / min. In this stage, the reaction is close to completion, and the slow addition of sulfuryl chloride can further promote the complete reaction, avoid excessive chlorination, and reduce unnecessary by-products.

[0056] By dividing the addition rate of sulfuryl chloride into three stages, the progress of the reaction can be accurately controlled to ensure that the synthesis of chloro-o-cresol has high selectivity and yield.

[0057] In step S2, the reaction of sulfuryl chloride and o-cresol can be expressed as:

[0058] C 7 H 8 O+SO 2 Cl 2 →C 7 H 7 C lO+SO 2 +HCl

[0059] Among them, C 7 H 8 O is o-cresol, SO 2 Cl 2 is sulfuryl chloride, C 7 H 7 C lO is p-chloro-o-cresol, SO 2By gradually adding sulfuryl chloride, the reaction can maintain high selectivity at different stages and reduce the formation of by-products.

[0060] According to the technical solution of the present invention, step S3 is distillation and product separation:

[0061] In step S3, the reaction mixture is processed via a rectifying tower, and the main purpose of rectification is to separate the target product p-chloro-o-cresol from unreacted raw materials, solvents and by-products. The reaction liquid may contain unreacted o-cresol, ethylene dichloride, sulfuryl chloride residues and by-products (such as sulfur dioxide and hydrogen chloride). The boiling points of these materials are different, so rectification can separate them from p-chloro-o-cresol by controlling temperature and pressure.

[0062] In the distillation process, the reaction mixture is first heated to evaporate. Since para-chloro-o-cresol has a high boiling point (about 174°C), while other solvents and by-products have lower boiling points (for example, the boiling point of ethylene dichloride is 83.5°C, and the boiling point of unreacted o-cresol is about 181°C), the target product can be effectively separated from other components by adjusting the temperature in the tower.

[0063] In order to efficiently separate the products, the operating conditions of the distillation tower need to be adjusted according to the specific composition of the reaction solution. The operating temperature of the distillation tower should be controlled within the boiling point range of the target product (about 170℃~180℃), and appropriate pressure should be used to improve the separation efficiency.

[0064] During the distillation process, the solvent (such as ethylene dichloride) and by-products (sulfur dioxide, hydrogen chloride, etc.) will be separated and can be recycled. The unreacted o-cresol and solvent will be refluxed through the top of the tower, and the unseparated substances such as sulfuryl chloride can be removed through the bottom of the tower. In addition, by recovering the ethylene dichloride and sulfuryl chloride residues volatilized in the tower, it helps to improve the utilization rate of the reactants and reduce environmental pollution.

[0065] After the reaction is completed, the liquid separated by the distillation tower mainly includes p-chloro-o-cresol and a small amount of impurities. For the p-chloro-o-cresol distilled out, further purification is required. Usually, this part of the crude product needs to go through further purification steps, such as recrystallization or other purification methods, to remove remaining impurities, to obtain final high-purity p-chloro-o-cresol.

[0066] Generally speaking, in the process of the present invention, o-cresol is mixed with ethylene dichloride and a catalyst, and reacts with sulfuryl chloride under temperature control conditions to generate p-chloro-o-cresol. The addition of sulfuryl chloride effectively improves the selectivity of the reaction by controlling the rate in stages, and avoids the generation of by-products. After the reaction is completed, the product is separated from the unreacted raw materials and by-products using a distillation technique, and finally high-purity p-chloro-o-cresol is obtained. The process is simple to operate, has mild reaction conditions, is suitable for large-scale production, and has good environmental protection and high efficiency.

[0067] Correspondingly, the present invention also provides a continuous preparation system of 4-chloro-o-cresol. The preparation system of the present invention will be described below in the form of the process flow of the present invention.

[0068] The continuous preparation system of p-chloro-o-cresol of the present invention mainly comprises a reaction kettle, a degassing device, a distillation tower and a tail gas treatment unit. The system realizes the efficient synthesis of p-chloro-o-cresol through the mutual cooperation of various devices, and ensures that the waste gas generated during the reaction process is effectively treated and recovered.

[0069] Reactor:

[0070] The reactor is used for the mixed reaction of o-cresol, ethylene dichloride, catalyst and sulfuryl chloride. The reactor should have a good temperature control system to ensure that the reaction temperature is controlled in an appropriate range (5-15°C) to ensure high selectivity of the reaction. The stirring device in the reactor can keep the raw materials uniformly mixed and promote full contact of the reactants.

[0071] During the reaction, ethylene dichloride acts as a solvent to help o-cresol dissolve and promote the reaction. The addition of a catalyst promotes the reaction of o-cresol with sulfuryl chloride, ensuring the smooth progress of the chlorination process. The para-chloro-o-cresol generated by the reaction will be separated in the subsequent distillation process.

[0072] Degassing device:

[0073] The degasser is connected to the reactor and is mainly used to remove volatile gases generated during the reaction, such as unreacted sulfuryl chloride, ethylene dichloride, and gas components in by-products. During the reaction, some gases may affect subsequent reactions or pollute the environment, so they need to be effectively removed by the degasser.

[0074] The degassing device introduces the volatile gases in the reactor into a special treatment device through a pipeline, which not only reduces the emission of pollutants but also ensures the stability of the atmosphere in the reactor.

[0075] Distillation tower:

[0076] The main function of the distillation tower is to separate the p-chloro-o-cresol in the reaction liquid from the unreacted raw materials, solvents and by-products. Through the operation of the distillation tower, the target product can be effectively separated and the unwanted impurities can be removed.

[0077] After the reaction is completed, the reaction liquid is sent to a distillation tower, and the temperature and pressure in the tower are adjusted to purify the para-chloro-o-cresol by utilizing the difference in boiling points of different components. The temperature in the tower is usually controlled near the boiling point of the target product para-chloro-o-cresol (about 174°C). The distillation tower not only separates para-chloro-o-cresol from unreacted o-cresol and dichloroethylene, but also recovers light components (such as unreacted solvents) and refluxes them to the reactor through the top of the tower, thereby improving resource utilization.

[0078] Exhaust treatment unit:

[0079] The tail gas treatment unit is an environmental protection facility in the preparation system of the present invention, which is mainly used to perform multi-stage adsorption, absorption and drying treatment on the tail gas generated during the reaction. The unit ensures that the harmful gases released during the reaction are effectively treated to reduce pollution to the environment.

[0080] The exhaust gas treatment unit includes the following equipment:

[0081] Secondary molecular sieve device:

[0082] The device is connected to the reactor and degassing reactor through pipelines and is used to adsorb the tail gas generated during the reaction. The secondary molecular sieve can adsorb moisture, organic solvents and other soluble gases in the gas, thereby improving the purification efficiency of the tail gas. The gas treated by the secondary molecular sieve will be returned to the reactor to further improve the utilization rate of the solvent.

[0083] Three-stage falling film water absorption device:

[0084] The tail gas after adsorption treatment by the secondary molecular sieve device will enter the third-stage falling film water absorption device through a pipeline. In this device, the acidic components in the gas (such as sulfur dioxide) will be absorbed by contact with water, thereby reducing the emission of harmful gases. The function of the falling film water absorption device is to efficiently absorb the water-soluble components in the gas.

[0085] Secondary sulfuric acid drying device:

[0086] The tail gas treated by the three-stage falling film water absorption device will be transported to the secondary sulfuric acid drying device. In this device, the moisture in the tail gas is further removed to prevent the moisture from affecting subsequent treatment and equipment. The secondary sulfuric acid drying device removes moisture from the gas through adsorption and drying processes.

[0087] Refrigeration recovery device:

[0088] The treated tail gas then enters the refrigeration recovery device, where the usable gas components are recovered through low-temperature condensation. The device can recover reusable components such as ethylene dichloride, further improving resource utilization.

[0089] Secondary alkali absorption device:

[0090] Finally, the tail gas treated by the refrigeration recovery device will enter the secondary alkali absorption device. This device is used to absorb the acidic components in the gas to ensure that the tail gas emissions meet environmental standards. Through this multi-stage tail gas treatment system, harmful substances in the tail gas are effectively removed to meet environmental emission requirements.

[0091] The preparation system of the present invention realizes the efficient preparation of chloro-o-cresol through the coordinated work of multiple devices. The combination of the reactor with the degassing device, the distillation tower and the tail gas treatment unit ensures the efficient progress of the reaction and the satisfaction of environmental protection requirements. The distillation tower effectively separates the target product, and the multi-stage treatment of the tail gas treatment unit ensures that the harmful substances in the tail gas are fully adsorbed, absorbed and dried, achieving the dual effects of environmental protection and resource recovery. The design of this system is reasonable, and an efficient and low-pollution preparation process can be realized in industrial production.

[0092] In order to better understand the present invention, the present invention is described in detail below in conjunction with specific embodiments.

[0093] Embodiment 1:

[0094] 2200 kg of molten o-cresol was added into a 5000 L reactor, and then 2000 kg of ethylene dichloride and 1.2 kg of catalyst (ferric chloride) were added respectively.

[0095] The reaction temperature was controlled at 10°C, and sulfuryl chloride was added in stages at different rates according to the reaction time (controlled at 12 hours):

[0096] In the first 4 hours, 9 kg of sulfuryl chloride was added per minute, and a total of 2160 kg was added.

[0097] Over the next 3 hours, 3 kg of sulfuryl chloride was added per minute, for a total of 540 kg.

[0098] During the last 5 hours, 1 kg of sulfuryl chloride was added per minute, and a total of 300 kg was added.

[0099] The total amount of sulfuryl chloride added was 3000 kg.

[0100] After the reaction was completed, the reaction solution was subjected to liquid chromatography detection, and the crude product obtained had: p-chloro-o-cresol accounting for 94 wt % and isomer content of 5.75 wt %.

[0101] The tail gas produced by the reaction is condensed through a condenser to remove trace products, then adsorbed through a secondary molecular sieve to remove organic matter, and then treated through a tertiary falling film water absorption device.

[0102] The purity of the product after distillation is 99.5wt% of p-chloro-o-cresol, and the purity of 6-chloro-o-cresol in the reaction solution reaches 99.5wt%.

[0103] Embodiment 2:

[0104] 1800 kg of o-cresol and 1500 kg of ethylene dichloride were mixed and added into a reactor, and diphenyl sulfide was added as a catalyst (accounting for 2% of the mass of o-cresol).

[0105] The reaction temperature was set to 12°C, the reaction time was controlled to 10 hours, and sulfuryl chloride was added in stages at the following rates:

[0106] In the first to third hours, 7 kg of sulfuryl chloride was added per minute, and a total of 1890 kg was added.

[0107] During the 4th to 6th hour, 2 kg of sulfuryl chloride was added per minute, and a total of 360 kg was added.

[0108] During the last hour, 1 kg of sulfuryl chloride was added per minute, and 60 kg in total was added.

[0109] The total amount added was 2310 kg of sulfuryl chloride.

[0110] The purity of the p-chloro-o-cresol obtained after distillation separation is 98.7 wt %, and the by-products of hydrogen chloride and sulfur dioxide are recovered through a tail gas treatment system.

[0111] When the distillation tower is operated, 6-chloro-o-cresol is separated by adjusting the reflux ratio, and then separated and recovered after condensation.

[0112] Embodiment 3:

[0113] 2500 kg of o-cresol and 2300 kg of ethylene dichloride were added into a 10000 L reactor, and aluminum chloride was added as a catalyst (1.5%).

[0114] The reaction temperature was controlled at 8°C, the reaction time was controlled at 12 hours, and sulfuryl chloride was added in stages at the following rates:

[0115] During the first to fourth hours, 8 kg of sulfuryl chloride was added per minute, and a total of 1920 kg was added.

[0116] During the 5th to 7th hours, 4 kg of sulfuryl chloride was added per minute, and a total of 672 kg was added.

[0117] During the last hour, 2 kg of sulfuryl chloride was added per minute, and 120 kg in total was added.

[0118] The total amount of sulfuryl chloride added was 2712 kg.

[0119] After the reaction was completed, the product was analyzed by liquid chromatography, and the content of p-chloro-o-cresol was 95 wt %, and the content of isomers was 4.5 wt %.

[0120] The tail gas produced by the reaction is condensed to remove water-soluble components, and then purified by a secondary molecular sieve and a tertiary falling film water absorption device.

[0121] The purity of the product after distillation is 99.8wt% of p-chloro-o-cresol, and the purity of the separated 6-chloro-o-cresol is 99.3wt%.

[0122] Embodiment 4:

[0123] 1500 kg of o-cresol and 1400 kg of ethylene dichloride were mixed and added into a 3000 L reactor, and ferric chloride catalyst (2%) was added.

[0124] The reaction temperature was controlled at 6°C, the reaction time was controlled at 8 hours, and sulfuryl chloride was added in stages:

[0125] In the first 1-2 hours, 10 kg of sulfuryl chloride was added per minute, and a total of 1200 kg was added.

[0126] During the 3rd to 5th hours, 5 kg of sulfuryl chloride was added per minute, and a total of 900 kg was added.

[0127] During the last 2 hours, 3 kg of sulfuryl chloride was added per minute, and a total of 360 kg was added.

[0128] The total amount of sulfuryl chloride added was 2460 kg.

[0129] After the reaction, the results of liquid chromatography analysis showed that p-chloro-o-cresol accounted for 93 wt % and the isomer content was 6 wt %.

[0130] The tail gas produced by the reaction is condensed to remove sulfur dioxide, and the sulfur dioxide is liquefied and stored through a refrigeration recovery device. The treated tail gas is finally discharged through a secondary alkali absorption device.

[0131] The purity of p-chloro-o-cresol obtained by separation in a distillation tower was 99.5 wt %, and the purity of 6-chloro-o-cresol in the reaction solution reached 99.3 wt %.

[0132] Embodiment 5:

[0133] 1000 kg of o-cresol and 800 kg of ethylene dichloride were mixed and added into a 3000 L reactor, and aluminum trichloride catalyst (2%) was added.

[0134] The reaction temperature was controlled at 10°C, the reaction time was controlled at 9 hours, and sulfuryl chloride was added in stages:

[0135] In the first to third hours, 12 kg of sulfuryl chloride was added per minute, and a total of 2160 kg was added.

[0136] In the 4th to 5th hour, 6 kg of sulfuryl chloride was added per minute, and a total of 360 kg was added.

[0137] During the last 2 hours, 2 kg of sulfuryl chloride was added per minute, and 240 kg in total was added.

[0138] The total amount of sulfuryl chloride added was 2760 kg.

[0139] After the reaction was completed, liquid chromatography analysis was performed to obtain a p-chloro-o-cresol content of 94.5 wt % and an isomer content of 5 wt %.

[0140] The tail gas produced by the reaction is first adsorbed by a secondary molecular sieve and then further treated by a tertiary falling film water absorption device.

[0141] After distillation, the purity of the obtained p-chloro-o-cresol is 99.6wt%, and the by-products are processed through a condensation and recovery device, and impurities are effectively removed.

[0142] Embodiment 6:

[0143] 2000 kg of o-cresol and 1900 kg of ethylene dichloride were added into a 6000 L reactor, and ferric chloride catalyst (1.8%) was added.

[0144] The reaction temperature was controlled at 8°C, the reaction time was controlled at 10 hours, and sulfuryl chloride was added in stages:

[0145] In the first to fourth hours, 9 kg of sulfuryl chloride was added per minute, and a total of 2160 kg was added.

[0146] In the 5th to 6th hour, 4 kg of sulfuryl chloride was added per minute, and a total of 480 kg was added.

[0147] During the last hour, 2 kg of sulfuryl chloride was added per minute, and 120 kg in total was added.

[0148] The total amount of sulfuryl chloride added was 2760 kg.

[0149] After the reaction was completed, liquid chromatography analysis was performed to obtain a p-chloro-o-cresol content of 94.5 wt % and an isomer content of 5 wt %.

[0150] The tail gas produced by the reaction is firstly treated by a secondary molecular sieve to remove organic matter, then treated by a tertiary falling film water absorption device, and finally the recovered gas is collected by a refrigeration recovery device.

[0151] The purity of the p-chloro-o-cresol obtained by separation in a distillation tower is 99.5 wt %, and the purity of the separated 6-chloro-o-cresol is 99.2 wt %.

[0152] Comparative Example 1:

[0153] Compared with Example 6, the addition rate of sulfuryl chloride was 15 kg per minute in the first 4 hours, and the remaining steps were the same.

[0154] Comparative Example 2:

[0155] Compared with Example 6, the temperature was controlled at 20°C, and the other conditions were the same.

[0156] Comparative Example 3:

[0157] Compared with Example 6, the ratio of dichloroethylene to o-cresol in the reaction kettle is 1:0.8, and the other conditions are the same.

[0158] Comparative Example 4:

[0159] Compared with Example 6, the amount of the catalyst used is 0.5% of the mass of o-cresol, and the other steps are the same.

[0160] Test Example 1:

[0161] Compare the differences in purity, selectivity and reaction efficiency of the products of Example 6 and Comparative Example 2.

[0162] Experimental methods:

[0163] The content of p-chloro-o-cresol, the content of isomers and the formation of by-products in the product were analyzed by liquid chromatography.

[0164] Record the reaction time and product quality at different temperatures, and compare the product purity and by-product formation.

[0165] After the experiment, the reactants are cooled and separated, and the products are distilled and purified.

[0166] The test results are shown in the following table:

[0167]

[0168] As can be seen from the experimental data, in Example 6 (10°C), the purity of para-chloro-o-cresol is higher (94.2%), and the generation of by-products and isomers is less. This result shows that the lower reaction temperature effectively controls the rate of reaction and maintains the high selectivity of the reaction. At a lower temperature, the reaction rate is slower, and the reaction of o-cresol and sulfuryl chloride is more gentle, which makes the generation of para-chloro-o-cresol more stable, and the generation of by-products (such as hydrogen chloride and sulfur dioxide) is also relatively less. According to the reaction mechanism, the lower temperature helps to suppress unnecessary excessive chlorination reaction, ensures that the reaction is carried out at the desired position (para-chlorination), thereby improving the selectivity of the target product.

[0169] In Comparative Example 2 (20°C), the increase in temperature caused the purity of para-chloro-o-cresol to drop to 89.6%, and the increase in isomer content and by-product content. Higher temperature accelerates the rate of reaction, but also causes excessive reaction, so that more chlorination reaction of o-cresol occurs, generating multiple chlorinated isomers and other by-products. According to the reaction mechanism, when the temperature rises, the reaction rate of sulfuryl chloride and o-cresol is accelerated, which improves the conversion rate of o-cresol, but also increases unwanted side reactions, resulting in an imbalance in the ratio of target product and by-products. Especially at higher temperatures, the reaction may become less selective, resulting in the generation of polychlorinated products.

[0170] The result of this experiment has verified the important role of temperature in controlling reaction selectivity and product purity.In embodiment 6, 10 ℃ temperature condition makes reaction remain in a relatively ideal scope, thereby obtains the p-chloro-o-cresol of higher purity.This is because at this temperature, reaction will not be too violent, can effectively avoid the generation and polychlorination of by product.On the contrary, although the use of higher temperature (20 ℃) ​​has accelerated reaction, it has caused the reduction of selectivity and the generation of by product, and illustrates that the control of temperature has vital influence on the selectivity of reaction and the final purity of product.

[0171] Test Example 2:

[0172] The differences in purity, selectivity and reaction efficiency of the products of Example 6 and Comparative Example 1 were compared.

[0173] Experimental methods:

[0174] The purity of the product, especially the ratio of p-chloro-o-cresol and by-products, was analyzed by liquid chromatography (HPLC).

[0175] The differences in the products of rapid addition of sulfuryl chloride (15 kg per minute) and staged addition of sulfuryl chloride (9 kg / min, 3 kg / min, 1 kg / min) were compared, and the formation of by-products was analyzed.

[0176] The test results are shown in the following table:

[0177]

[0178]

[0179] As can be seen from the experimental data, the staged addition of sulfuryl chloride (9→3→1 kg / min) in Example 6 effectively controls the reaction process, and ensures the high purity (94.2%) and lower isomer content (5.75%) of para-chloro-o-cresol under mild conditions. This mode of progressively adding sulfuryl chloride helps to avoid too violent reaction, reduces the generation of polychlorinated products, and thus maintains the selectivity of para-chloro-o-cresol. This is consistent with the reaction mechanism, and the progressive addition of sulfuryl chloride reduces the risk of excessive chlorination, so that when o-cresol reacts at a lower temperature, para-chlorination is preferentially carried out, avoiding excessive chlorination or forming unwanted by-products.

[0180] In contrast, in Comparative Example 1, the rapid addition of sulfuryl chloride (15 kg / min) resulted in an overly violent reaction. The rapid addition of sulfuryl chloride not only accelerated the reaction rate, but also increased the generation of by-products (1.5%), and significantly increased the content of isomers (8.1%). According to the reaction mechanism, the too rapid addition of sulfuryl chloride may lead to overreaction, and the chlorination site of o-cresol becomes no longer selective, thereby generating a variety of isomers and by-products. The high reaction rate may also lead to the occurrence of side reactions, further reducing the selectivity of the target product.

[0181] This experimental result verifies the significant influence of reaction rate and sulfuryl chloride addition rate on product purity. The method of adding sulfuryl chloride in stages helps to maintain the stability and high selectivity of the reaction, ensuring that the reaction preferentially proceeds to para-chlorination at a lower temperature, thereby obtaining high-purity para-chloro-o-cresol. Although the method of rapidly adding sulfuryl chloride speeds up the reaction process, it sacrifices the purity and selectivity of the product and generates more isomers and by-products.

[0182] Test Example 3:

[0183] Compare the differences in purity, selectivity and reaction efficiency of the products of Example 6 and Comparative Example 4.

[0184] Experimental methods:

[0185] The purity of the target product, especially the ratio of p-chloro-o-cresol and by-products, was analyzed by liquid chromatography (HPLC).

[0186] The two groups of reactions with different catalyst dosages were compared to analyze the effect of catalyst dosage on reaction rate, product selectivity and by-product formation.

[0187] The test results are shown in the following table:

[0188]

[0189] As can be seen from the experimental data, in Example 6, using a higher catalyst level (1.8%) helps to improve reaction rate and selectivity, product purity has reached 94.2%, isomer content is lower (5.75%), and the generation of by-products is also less (0.2%). This phenomenon is closely related to the reaction mechanism, and the catalyst can activate the chlorine atom in the sulfuryl chloride as the effect of Lewis acid, improving the speed of the nucleophilic substitution reaction between it and o-cresol. Higher catalyst levels can provide more active sites, so that the reaction is carried out more completely, thereby ensuring high selectivity and high purity to chloro-o-cresol.

[0190] In contrast, in Comparative Example 4, the catalyst dosage was only 0.5%, resulting in a slowed reaction rate, a reduced product purity of 89.5%, an increased isomer content of 8.1%, and an increased generation of by-products (1.5%). In the case of low catalyst dosage, the activation of sulfuryl chloride was insufficient, resulting in an incomplete or inefficient reaction of o-cresol with sulfuryl chloride. This caused the reaction to be biased toward polychlorination or to produce other unwanted by-products, thereby affecting the purity and selectivity of the target product.

[0191] According to the reaction mechanism, when sulfuryl chloride reacts with o-cresol, the catalyst promotes the increase of the electropositivity of sulfuryl chloride, so that the reaction occurs more selectively at the para position of o-cresol. A lower catalyst dosage cannot effectively activate sulfuryl chloride, resulting in a slow reaction, and the reactant fails to be fully converted into p-chloro-o-cresol, and more by-products are generated. By increasing the catalyst dosage, the reaction rate and selectivity can be improved, thereby avoiding the generation of by-products and obtaining p-chloro-o-cresol of higher purity. Therefore, the dosage of the catalyst directly determines the efficiency of the reaction, the purity of the product, and the generation of by-products.

[0192] Test Example 4:

[0193] Compare the differences in purity, selectivity and reaction efficiency of the products of Example 6 and Comparative Example 3.

[0194] Experimental methods:

[0195] The purity of the target product, especially the ratio of p-chloro-o-cresol and by-products, was analyzed by liquid chromatography (HPLC).

[0196] Compare the reaction effects under different solvent ratios and observe the influence of solvent ratio on reaction efficiency, product purity and by-product formation.

[0197] The test results are shown in the following table:

[0198]

[0199] According to experimental data, when the solvent ratio among embodiment 6 was 1:1.05, the purity of para-chloro-o-cresol was 94.2%, and by-product generation was less (0.2%), and isomer content was 5.75%. This highly purified product shows that suitable solvent ratio helps the abundant dissolving and contact of o-cresol and sulfuryl chloride. In the reaction mechanism, the effect of solvent is to provide an environment suitable for, so that reactant is evenly distributed in solvent, promotes the reaction of o-cresol and sulfuryl chloride. By keeping reasonable solvent ratio, the reaction of o-cresol is more even, thereby improved the selectivity of target product, reduced the generation of by-product.

[0200] In Comparative Example 3, the solvent ratio is 1:0.8, which causes the solubility of o-cresol to decrease, affects the completeness of the reaction, and ultimately causes the purity of p-chloro-o-cresol to drop to 89.6%, the by-product content to rise to 1.8%, and the isomer content to be 8.2%. According to the reaction mechanism, a relatively small solvent ratio makes the contact of o-cresol and sulfuryl chloride uneven, which may lead to incomplete reaction or the occurrence of polychlorination reaction. The insufficient amount of solvent will cause the reactants to gather in local areas, inhibit the efficiency of the reaction, and increase the amount of by-products.

[0201] This result further verifies the importance of solvent in the reaction. The right amount of solvent not only helps to improve the solubility of the reactants, but also can evenly distribute the reactants to ensure the smooth progress of the reaction. Too low a solvent ratio leads to insufficient dissolution of o-cresol, making the reaction incomplete, thereby affecting the formation of p-chloro-o-cresol and the purity of the product. Therefore, a reasonable solvent ratio is crucial to improving the purity, selectivity and efficiency of the reaction of the product.

[0202] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A continuous preparation process of para-chloro-o-cresol, characterized in that: The following steps are involved: a) adding ethylene dichloride to molten o-cresol and adding a catalyst; b) Under the temperature condition of 5 to 15° C., controlling the rate of addition of sulfuryl chloride according to the reaction stage, specifically comprising: In the first stage, sulfuryl chloride is added at a rate of 6-15 kg / min; In the second stage, sulfuryl chloride is added at a rate of 2 to 5 kg / min; In the third stage, sulfuryl chloride is added at a rate of 0.5 to 1.5 kg / min; c) After the reaction is completed, the reaction liquid is distilled and purified to obtain p-chloro-o-cresol.

2. A continuous preparation process for para-chloro-o-cresol according to claim 1, characterized in that: The catalyst is one of diphenyl sulfide, ferric chloride or aluminum chloride.

3. A continuous preparation process for para-chloro-o-cresol according to claim 1, characterized in that: In step b), the first stage is 1 to 4 hours after the addition of sulfuryl chloride, the second stage is 5 to 7 hours after the addition of sulfuryl chloride, and the third stage is the remaining time; the total reaction time is controlled to be 8 to 15 hours.

4. A continuous preparation process for para-chloro-o-cresol according to claim 3, characterized in that: In the first stage, the rate of addition of sulfuryl chloride is 9 kg / min; in the second stage, the rate of addition of sulfuryl chloride is 3 kg / min; in the third stage, the rate of addition of sulfuryl chloride is 1 kg / min.

5. A continuous preparation process of para-chloro-o-cresol according to claim 1, characterized in that: In step a), the mass ratio of the ethylene dichloride to o-cresol is 1-3:1-4.

6. A continuous preparation process of p-chloro-o-cresol according to claim 5, characterized in that: In step a), the mass ratio of the ethylene dichloride to o-cresol is 1:1.

1.

7. A continuous preparation process of p-chloro-o-cresol according to claim 1, characterized in that: In step b), the mass ratio of the added sulfuryl chloride to o-cresol is 1-2:0.5-1.

5.

8. A continuous preparation process for para-chloro-o-cresol according to claim 7, characterized in that: In step b), the mass ratio of the added sulfuryl chloride to o-cresol is 1.275:

1.

9. A continuous preparation system of para-chloro-o-cresol, characterized in that: include: A reaction kettle is used to mix o-cresol, ethylene dichloride, a catalyst and sulfuryl chloride and react under controlled temperature conditions; A degassing device, connected to the reactor, is used to remove volatile gases generated during the reaction and reduce pollution; A distillation tower, connected to the degassing device, is used to separate the reaction liquid by distillation, extract pure para-chloro-o-cresol, and reflux the unreacted light components to the reactor; The tail gas treatment unit is used to carry out multi-stage adsorption, absorption and drying treatment on the tail gas generated during the reaction.

10. The continuous preparation system of p-chloro-o-cresol according to claim 9, characterized in that: The tail gas treatment device includes a secondary molecular sieve device, a tertiary falling film water absorption device, a secondary sulfuric acid drying device, a refrigeration recovery device and a secondary alkali absorption device; The reactor and the degassing reactor are both connected to the secondary molecular sieve through pipelines, and the tail gas in the reactor and the degassing reactor is sent to the secondary molecular sieve device for adsorption; The liquid after adsorption treatment by the secondary molecular sieve device is returned to the reactor; The secondary molecular sieve device is connected to the tertiary falling film water absorption device through a pipeline, and the tail gas treated by the secondary molecular sieve device is sent to the tertiary falling film water absorption device for treatment; The three-stage falling film water absorption device is connected to the two-stage sulfuric acid drying device through a pipeline, and the tail gas treated by the three-stage falling film water absorption device is sent to the two-stage sulfuric acid drying device for treatment; The secondary sulfuric acid drying device is connected to the refrigeration recovery device through a pipeline, and the tail gas treated by the secondary sulfuric acid drying device is sent to the refrigeration recovery device for treatment; The refrigeration recovery device is connected to the secondary alkali absorption device through a pipeline. The tail gas treated by the refrigeration recovery device is treated by the secondary alkali absorption device and then discharged.

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